Sound recording and reproduction



June 4, 1929. J, POMERQY 1,715,863

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R. J. POMEROY SOUND RECORDING AND REPRODUCTION Filed Aug. 9, 1927 4 Sheets-Sheet OSCILLA T/NG C/ECU/T CEKSML go/yreoL I SPEA/(E Patented June 4, 1929.

UNITED STATES PATENT ori ice.

\ ROY J. FOMEROY, OF HOLLYWOOD, CALIFORNIA, ASSIGNOR OF ONE-HALF TO PARA- MOUNT FAMOUS LASKY CORPORATION, OF LOS AN GELES, CALIFORNIA, A CORPORA- TION 0F new YORK.

SOUND RECORDING AND REPRODUCTION.

Application filed August 9, 1927. Serial No. 211,834.

This invention has to do with the recording and reproduction of sound; and the 1nvention is best exemplified as a system using a sound record of the photographic type, the invention making use of certain characteristics of that type of sound record which so far as my knowledge goes, has not heretofore been used for sound reproduction.

As is well understood in the art, photographic sound records have been produced 1n various manners and have then been reproduced by subjecting a selenium cell or a photoelectric cell to a beam of light intercepted and modified by the photographic sound rec- 0rd, thus making use of the varying light transmissivity of such record.

In contradistinction to all the past practlces ofwhich I am aware, my system first provides a sound record that has what may be termed a varying capacity, or a varying dielectric characteristic, and then make use of those varying characteristics to vary the effective capacity of a condenser assembly, using such resulting varying. condenser capacity for actuating a system which includes a sound vibration producing element. The actual final production of sound in this sound vibration producing element may typically be in the form of a speaker, and the system may also include oscillating and amplifying circuits which feed the speaker.

Although my present system is not necessarily limited to the use of photographic sound records such as are now known, re-

quiring only a record in which the sound vibrations are represented by record parts or elements having a varying di-electric or capacity characteristic, the invention may well use, and. is at present most readily illustrated by use of, certain types of photographic sound records. Consequently in describing the in-. vention I shall illustratively describe the use of certain types of such photographic sound records.

Inthe drawings;

Fig. l-is a diagram illustrating a complete "reproducing system;

Fig. 2 is an enlarged diagrammatic section taken on line 2-2 of Fig-1';

Figs. 3, 4 and 5 are diagrams indicating several typical manners in which the record may be made.

Figs. 6, 7 and 8 are diagrams illustrating modified-manners of using other types of record.

In order to describe a typical record I shall refer first to Fig. 3. Here a glow-tube is indicated diagrammatically at 10. In producing a record this glow tube will be energized in a circuit whose potential varies in accordance with the sound vibrations wished to be recorded. Systems for thus operating a glow tube, or a source of illumination of any character, are so well known as to need no description here. Typically such system may embody a microphone which receives sound initially, the current from the microphone being amplified through an amplifying circuit and the glow tube fed from the output of that amplifying circuit. The nature of the glow tube is such that with variation of potential the glow indicated at 10 in Fig. 3 varies in length. A slit such as indicated at v11 may be used in connection with such a tube so that the image cast upon'film 12 by lens 13 will be of constant width, the width controlled by the slit, and of varying length. Thus, presuming that film 12 is moved lengthwise in the relative direction indicated, it will, upon development, show a series of shaded images such as are diagrammatically indicated by the lines at 15, one end of all the images being in or forming a straight line as shown at 16 and the other end of the image series forming an undulating line as indicated at 17. The several images of the series may be juxtaposed, or substantially so, or they may be fairly well separated in the direction of length and movement of the film, depend ing upon the speed of vibration of the right in the glow tube and upon the speed of movement of the film. In-any case the distance between images in the direction of movement of the film will represent the speed of vibration (the pitch of the sound), the length of the image will represent amplitude of vibration (the volume of the sound) and the curve 17 represented by the ends of the images will represent the characteristics of the sound.

Also the several successive images may be,

when develo ed, of somewhat varying den- ;sity, due to t e glow becoming brighter as it' becomes longer. Such varying densities may therefore at least partially represent ampli- I particular point in the whole composite image is controlled by and thus represents all of the characteristics of the initial sound. The usual method of reproduction of such a record depends upon the varying light transmissivity of such a record due to its varying local amounts of developed silver; but my method of reproduction depends, as I have said, upon other distinct characteristics of 'those varying amounts of reduced silver.

In reproducing such a record it may be run between two small condenser plates located on opposite sides of the film at a suit able distance from each other. These condenserplates may preferably be in the form of narrow bars or wires, stiff enough to be supported rigidly in definite relationship to each other and to the film; and preferably the width of these small plates (their dimension in a direction lengthwise of the film) will be not more than the width of a single image, or periodicity distance between images, on the film. As the film is run between these two condenser plates the effective capacity, of the condenser assembly is varied because of the variation of the nature of the di-electric between the two plates. From what I'have said concerning the record it will be readily understood that as the film is run between the two plates varying amounts of developed silver are at different times present between the two plates; the varying amounts of silver being due to the varying length dimensions of the several images and also'due perhaps somewhat totheir varying density. Fig. 2 shows in diagram, perhaps somewhat exaggeratedly, the varying thickness or density of metallic silver deposit 21.

The condenser formed by the two plates 20, with its intervening 'variable di-electric, is connected to the input circuit of an amplifying set, the two wires 25 and-26 ofthe input circuit being. connected to the two plates.'

This input circuit will include an inductance L which is coupled with the inductance L of an oscillating circuit ofany suitable type, the oscillating circuit as a whole being indicated by the letter 0. An oscillating current of definite periodicity is set up in the input circuit which includes the described condenser; and a sound wave is imposed upon that oscillating current by the varyingceffective capacity of the condenser. It is preferred to set up anoscillating current of comparatively high frequency as a given yaria tion incapacity will cause a larger variation of current than if a current of lower frequency were used; -.The oscillating current with the imposed sound wave which flows in the input. circuit is substantially similar to some sound Wave producing element, such as a speaker S. Control of the degree of amplification may of course be effected in anyof the manners common to amplify ng cir- Cl11tS,aI1d also the 'ma nitude or volume of the final sound productlon may be controlled by changing the normal capacity of the condenser assembly" or by changing the oscillating frequency. It is very simple for instance to change the distance between the two condenser plates 20. But it will be understood that in any and all variations of capacity of the condenser, either by way of adjustment or in sound reproducing operation, that capacity will be within the limits which must necessarily be observed, with any given inductance and resistance of the circuit, to insure oscillation. In other words, the circuit of the condenser'is always' an oscillating circuit, but its free periodicity is varied by the varying capacity, and it is the variation of its intrinsic periodicity, more or less in synchronism with the'periodicity of "the oscillations impressed on that circuit,

that varies the R. F. current flowing therein.

Thus, as an'illustration, suppose the constant oscillations are of 60 m. wave length. The intrinsic oscillations in the variable condenser circuit may then vary through a range either below 60 m. or above 60 III-L Any kind of record wherein the original sound is representedby elements having cor respondingly varying capacity of di-electric strength may be used in my system. It isnot necessary that a record contain-ing silver or any other metal be used; in fact there are certain advantages in using records containing other substances. In. using a silver-containing or similar record it is of coursenecessary that the successive images be large enough in proportion to the size of silver grains, or that the film be run fast enough,

. 'VVhatever those light sensitive substances are,

or whatever may be the resultant development or transformation products which form the final record, and regardless of whether the final record is visible or not, the varying amounts of development orother product in successive images W111 always lntroduce; at least to some degree, a varying factor of .5 capacitance or of dielectric characteristic,

which will be effective in my system. Generally speaking, no two different substances have exactly the same di-electric or capaci tance characteristic; and therefore any image substanceany substance different from the gelatin which it, in eifect, displaceswill introduce the varying characteristics on which the operation of my system depends.

Likewise it is of no particular concern in my system as to just how the records are them in such a way that they may be made use of to vary the effective capacity of a condenser assembly. lVithout attemptingin the least to exhaust even illustratively the possible variations in types of records I have in dicated diagrammatically in Figs. 3 and 4 the making of two other types of record.

/ For'instance in Fig. 4 the elements of a cathode ray tube are diagrammed, the two electrodes being indicated at 35 and 36. The

r'cathode ray passes through a slit 37 and plays upon and along the length of a luminiscent surface 38, creating a line of light which, vunder normal circumstances, is straight. By using two electromagnets 39 which are energized from the circuit 40, 41 carrying an audio frequency current, the line of light'in the cathode ray tube may be fluctuated or bent away from its normal straight path. If a slit 42 is then placed so that in the normal ray position the slit appears to be full of light, then as the cathode ray is deviated the image viewed through the slit. by lens 43 will appear as a wedge. which may have a fixed base at one end of thes1it, but is of va- 45 rying length. Such single images are indicatedat I in Fig. 4. The resultant composite or aggregate image produced on the moving film when the film is developed will be somewhat similar in appearance to thatproduced so by the glow tube before described. Thus,

as before, the outline 17 through the tips of the successive images will represent the characteristics of sound, the lengths of the image will represent the amplitude of vibrations and the wavy outline will represent frequency and sound character.

In Fig. 5 I indicate the making of anothei form of record wherein only varying spacings between successive images and varyingdensities of those images are used.

For instance a filament light with afilament 50 may have its image thrown upon the traveling film'by a lens 51,8. slit 52 being used if desired. The successive images 15" on the film will beall of constant length but will vary in spacing and in density.

It will of course be understood that what I refer to as images are not in reality separate images, as if the film where being moved intermittently. The final composite image is actually made up of an infinite number of what may be called instant images.

I may also note that the showings of film images are here made in negative form, in illustrating both the production and reproduction of the film: The use of positives, or of duplicate negatives will, however, be well understood.

In'order further to illustrate other typical possibilities of my system I refer now to Figs. 6, 7 and 8.

In Fig. 6 a film 12 like that of Fig. 5 is illustrated wherein the record image 15 is made up, in appearance, of a plurality-oi shaded lines. Instead of using the record to v modify the di-electric element of the variable condenser, the record can be used in such a manner that its component images become one plate of the condenser. This would be especially trueof a record of that type shown in Fig. 6 where a film has been run fast enough that the component images, so to speak, are spaced more or less widely from each other, so that, between successive image areas that have comparatively high capacitance characteristics, there are intervening parts of the record that have relatively high resistance. Using a record of such a type, for instance, a small brush, indicated diagrammatically at 50, may be placed in such a position that it will contact successively with each component image asthe image that, as each component image comes into opposing relation to the condenser plate, it is connected into the circuit 25-26 so that it becomes in effect a plate of the condenser. In this. arrangement, as in all the other variations of my system, it is of course aimed to make the condenser action include, at any given instant,-substantially the same image area as was originally produced on the record at any given instant. In the form of Fig. 1 this is accomplished by having the width of the plates 20 correspond to the width of the instant image; and in the form shown in Fig. 6 plate 20 will also be made to correcomes opposite the condenser plate 20*; so

type is illustrated; Here the circuit 25 3-26 is connected directly into the oscillating circuit O which feeds, through'the coupled inductances L and L into a detector and amplifying circuit which may be substantially .the same as before described, but which is merely indicated in Fig. 7. ,In this case,

however, instead of running the film between the two condenser plates 22, it is run past" the edges of the plates so that, as the succes-3 sive image areas cross the space between the plates, they vary the effective capacity of the condenser made'up of those two plates. This variationfim'a be looked at either as a variation inthe e ective di-electric between the two plates, or as a variationin ashortcircuiting but high resistance between the two plates.

In Fig. 8 stillanother arrangement is illustrated. Here I show a film 12' having two complete records 15* and 15. Such a record,

a and its production and reproduction, are the subject-matter of my co-pending application S. N. 228,711, filed Oct. 26, 1927. I may here explain that such a double record may involve one record 15 ,"the same as any of the records hereinbefore explained, and acorresponding complementary record ;1-5 Such a record will have been made, for instance, by using two glow tube sets, such as shown in Fig. 3. One such set will be fed with one undulating cur- .rent and the other with a complementary undulating current, so that the two records 15 and 15 will be complements of each other, their outlines being identical but one record having a maximum image opposite a minimum image in the other record. Using such a record, one common condenser plate 20 may be located at one side of the film and a air of shorter condenser plates 20 and 20 located oppositely, the film running between them and plate 20, so that c0ndenser-20-2O is affect- I ed by record 15 and condenser 20-20 is affected by record 15. I Such a record lends itself readily to a balanced arrangement ofthe two condensers in a bridge circuit wherein the condenser actions aid and augment each other. Such a circuit-' ing is shown in Fig; 8 wherein plate 20 is connected into the center of two coupled induct ances L these being connected at their outer sides through wires 25, 26 to p1ate s 2Q .20, respectively. The circuit thus formed I -Figs. 7 and 8.

I claim: 1. In a system of sound reproduction, th combination of a sound record wherein sound vibrations are represented by portions of the record having varying dielectric characteristics, said sound record comprisingtwo com- 1 plete complementary sound wave representations, an electrical circuit including an input inductive w1nd1ng,.and a condenser assembly of which sald sound record forms a dielectric,

- said con-denser assembly comprising, a pair of.

condenser plates, one positioned overeach of said complementary sound wave representations, and a third plate positioned over both of said complementary sound waverepresentations, said first mentioned condenser plates being connected to opposite ends of the inductive winding, andsaid last, mentioned condenser plate being connected to a mid-point of the inductive winding.

2. In a system ofsoundreproduction, the combination of a sound record wherein sound vibrations are representedby portions of the record having varyingdielectric characteristics, said sound record comprising two complete complementary sound wave representations, an oscillating radio frequency circuit in eluding aninducti've winding and a condenser assembly of which said sound record forms a dielectric, said condenser assembly comprising, a pair of condenser plates, one positioned over each of said complementary sound wave-representations, and a third plate positioned over b'othof said complementary sound wave. representations, said first mentioned condenser plates being connected to opposite ends of the inductive winding, and, said last mentioned condenser plate being connected to a midpoint of the inductive winding, and K means for transforming the radio frequency current of said circuit into an audio frequency current and amplifying it. p In witness that Iclaim the foregoing I have I hereunto subscribed my name.

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